The invention relates generally to the field of digital imaging, and more particularly to optical three-dimensional imaging and mensuration systems for industrial applications.
Digital imaging systems acquire, or record, many two-dimensional images of a scene for various types of applications. One illustrative type of application is photogrammetry, in which information such as distances between points on objects in a scene, heights of such points above a reference level, and so forth, can be determined from measurements between and among points on the two-dimensional images that were acquired of the scene. Another type of application is generation of three-dimensional virtual reconstructions of objects in a scene from the two-dimensional images that were acquired of the scene. Such virtual reconstructions can be used, for example, for precise measurement of features of the reconstructed objects, comparisons between an actual object as represented by its reconstruction and the desired design for the object, and for other uses as will be apparent to those skilled in the art. In yet another application, virtual two-dimensional images of the scene can be generated from directions from which the digital imaging systems did not acquire actual images.
Typically, in any of these applications, it is necessary to use at least two images of a portion of a scene in order to, for example, generate a reconstruction of that portion of the scene. In addition, a digital imaging system may make use of more than two images which may increase accuracy. Although a digital imaging system can make use of a single camera to capture the images of the portion of the scene, some digital imaging systems make use of more than one camera, with the cameras being supported in fixed displacement and angular orientation relative to each other. One illustrative digital imaging system is described in U.S. Pat. No. 6,167,151, issued Dec. 26, 2000, in the names of Dan Albeck, et al., and entitled xe2x80x9cApparatus And Method For 3-Dimensional Surface Geometry Reconstruction,xe2x80x9d assigned to the assignee of this application, incorporated by reference.
If the portion of the scene that a digital imaging system reconstructs from one set of images is not the entire scene of interest, it may be necessary to move at least the cameras of the digital imaging system to other positions and angular orientations relative to the scene to enable them to capture images of the other portions. In that case, the digital imaging system will, for example, generate reconstructions of the portion of the scene based on the set of images that were acquired in each of the various positions. Each reconstruction will be relative to a coordinate system that, in turn, is related to the location(s) of the cameras from which the respective reconstruction was generated, and the digital imaging system can relate the reconstructions to a common xe2x80x9cglobalxe2x80x9d coordinate system to xe2x80x9cstitchxe2x80x9d the reconstructions together. This allows, for example, a feature in a portion of the scene that is present in one reconstruction to be related to a feature that is present in another reconstruction. Several illustrative methodologies for stitching reconstructions generated relative to respective coordinate systems are described in the aforementioned Albeck patent, and in U.S. patent application Ser. No. 09/606,054, filed Jun. 28, 2000, in the name of Tamir Shalom, now U.S. Pat. No. 6,556,705, entitled System And Method For Aligning A Locally-Reconstructed Three-Dimensional Object To A Global Coordinate System Using Partially-Detected Control Points, assigned to the assignee of this application and incorporated by reference. Generally, those methodologies make use of points on objects in the scene that are reconstructed in two reconstructions. In the methodology described in the Albeck patent, one reconstruction is stitched to another using reconstructions of the same points of the scene. In that case, the two reconstructions would need to overlap to enable them to be stitched together. In addition, in that case, the global coordinate system would be associated with the coordinate system associated with one of the reconstructions. In another methodology, described in the Shalom application, xe2x80x9ctargetsxe2x80x9d are provided in the scene whose positions relative to a global coordinate system are known. In that case, positions of the targets in the various reconstructions are used to align the reconstructions to the global coordinate system.
Digital imaging systems have generally been able to provide good results in environments in which environment variables such as temperature, humidity, mechanical vibrations, electromagnetic interference, and so forth, can be fairly rigidly controlled. Changes in temperature and humidity can, for example, cause rigs that provide support for cameras, illumination sources and the like to expand and contract undesirably, since expansion and contraction can change the positions and angular orientations of the cameras relative to each other. Mechanical vibration can arise when a rig moves the cameras, illumination sources and the like from one location and/or angular orientation relative to a scene, to another location and/or angular orientation. If mechanical vibration occurs, the digital imaging system may need to wait until the vibration subsides to allow the cameras to acquire the necessary images, which can unduly delay the acquisition. However, these problems, as well as others, can prevent digital imaging systems from being used in industrial environments, in particular in the manufacturing process, where such environmental variables cannot be rigidly controlled.
The invention provides a new and improved optical three-dimensional digital imaging and mensuration system for industrial applications.
In brief summary, the invention in one aspect provides an image acquisition arrangement for acquiring at least one image of at least one portion of a scene, the image acquisition arrangement comprising a least one camera and at least one illumination source controlled by a control module. In that aspect, the at least one camera includes an image recording medium and at least one shutter controllable to enable the image recording medium to acquire the at least one image. The at least one illumination source is configured to illuminate the at least one portion of the scene for a selected time period. The control module is configured to control the at least one camera and at least one illumination source to facilitate acquisition of the at least one image by the at least one camera, the control module being configured to enable the shutter of the at least one camera to, in turn, enable the image recording medium to acquire the at least one image and contemporaneously to enable the at least one illumination source to illuminate the at least one portion of the scene, the time period during which the shutter enables the image recording medium to acquire an image of the at least one portion of the scene being a function of the time period during which the at least one illumination source illuminates the scene.
In another aspect, the invention provides an image acquisition arrangement comprising a plurality of cameras mounted on a support, each camera having an image recording medium, the cameras and support being constructed of materials having respective coefficients of thermal expansion and configured to maintain the cameras"" image recording media in fixed relation to each other.
In yet another aspect, the invention provides an image acquisition arrangement comprising at least one camera comprising an image recording medium configured to generate signals in electrical form representative of an image, the image recording medium being housed in a housing, the housing being configured to shield the image recording medium from electromagnetic interference originating outside of the housing. In other aspects, other elements of the image acquisition arrangement, including power supplies that provide power to the at least one camera, and communication links linking the at least one camera to an image processing subsystem, are also relatively impervious to electromagnetic interference.